Vehicle engine systems such as those providing higher torque may utilize gasoline direct injection (GDI) to increase power delivery and engine performance. GDI fuel injectors in these vehicle engine systems demand fuel at higher pressure for direct injection to create enhanced atomization providing more efficient combustion. In one example, a GDI system can utilize an electrically driven lower pressure pump (also termed a lift pump) and a mechanically driven higher pressure pump (also termed a direct injection fuel pump) arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage. In many GDI applications the lift fuel pump initially pressurizes fuel from the fuel tank to a fuel passage coupling the lift pump and direct injection fuel pump, and the high-pressure or direct injection fuel pump may be used to further increase the pressure of fuel delivered to the fuel injectors.
In a single lift pump system, a lift pump is operated to pump fuel to port injectors or a direct injection fuel pump. Lift pumps may have large dynamic ranges to be capable of pumping fuel at a low pump rate, as at idling conditions, or at a high pump rate, as during high engine load conditions. Additionally, lift pump pumping efficiency is dependent upon the flow rate of the pump, where lower fuel flow rates correspond to lower pumping efficiencies. Often, an engine is operated at low fuel flow rate conditions, and so, a large capacity fuel pump may operate at low pumping efficiency during this time, wasting electrical energy. Alternatively, if a small capacity fuel pump is included in the engine fueling system instead of a larger capacity fuel pump, the smaller fuel pump may be unable to supply enough fuel during high engine load conditions, resulting in an engine torque output being below a desired engine torque. Some approaches aimed at reducing pump losses and increasing fuel delivery may include two fuel lift pumps.
However, the inventors herein have recognized potential issues with such systems. As one example, the two lift pumps may not be independently controlled, and even if they are, they may both operate during a majority of vehicle operation. When the lift pumps are both operated such that their flow rates are low, an imbalance may occur between the lift pumps where, the flow rate from one pump may become significantly reduced relative to the other pump. Thus, in some examples, although power may be supplied to both pumps, only one of the pumps may be pumping fuel. Thus, energy and fuel may be wasted providing power to the pump that is not pumping fuel or is pumping fuel at a reduced rate relative to the other pump.
In one example, the issues described above may be addressed by a method comprising, adjusting operation of a first lift pump based on a difference between a desired fuel rail pressure and a measured fuel rail pressure, and in response to one or more of an accelerator pedal tip-in, desired fuel rail pressure increasing above a threshold pressure, and the difference between the desired fuel rail pressure and the measured fuel rail pressure increasing by more than a threshold difference, powering on a second lift pump. In this way, fuel consumption may be reduced by only powering on the second lift pump when additional fuel pressure is needed, and when a desired fuel flow rate from the lift pumps is high.
In another representation, a method may comprise: generating a fuel pump command based on one or more of a desired fuel pressure, a difference between the desired fuel pressure and a measured fuel pressure, and a fuel injection amount, determining a first duty cycle for a first lift pump based on the fuel pump command, determining a second duty cycle for a second lift pump based on the fuel pump command, and adjusting operation of the first and second lift pumps based on the first and second duty cycles, respectively.
In another representation, a fuel system may comprise: a first lift pump, a second lift pump, a first lift pump module for regulating a first duty cycle of the first lift pump, a second lift pump module for regulating a second duty cycle of the second lift pump, and a controller in electrical communication with the first and second pump modules, where the controller may include computer-readable instruction stored in non-transitory memory for: generating a lift pump command signal based on a difference between a desired fuel rail pressure and a measured fuel rail pressure, and transmitting the lift pump command signal to the first lift pump module and second lift pump module.
In this way, fuel rail pressure may be more closely be matched to a desired fuel rail pressure by operating two lift pumps differently based on common input command from an engine controller. Further, a technical effect of reducing fuel consumption is achieved by operating a smaller lift pump when the difference between a desired fuel rail pressure and a measured fuel rail pressure is less than a threshold. Thus, by only operating both a first lift pump and second lift pump when the difference between the desired fuel rail pressure and the measured fuel rail pressure is greater than a threshold difference, energy consumption may be reduced, and the longevity of a lift pump may be increased. Further, an amount of electrical wiring and processing hardware may be reduced by differentially operating two lift pump given the same input command from an engine controller.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.